This invention relates generally to pay television systems and particularly to a method of operating a pay television system with provision for subscriber self-authorization to permit viewing of special pay per view programs.
While the inventive system and method will be described in a cable television environment, it will be appreciated that over-the-air television signalling systems can also benefit from the invention. In pay per view television systems selected channels or events, such as sports programs and the like, are generally made available to system subscribers for a fee in addition to that normally charged for the cable or subscription service. The invention provides a cable television system with subscriber terminals having authorization memories which the subscribers can self-authorize to view a special impulse pay per view (IPPV) feature. The invention further provides for two-way communication to enable polling of the individual subscriber terminal authorization memories to determine which, if any, IPPV programs have been "bought."
In pay television systems, each subscriber terminal is typically identified by a unique address which permits the cable head-end to selectively communicate with the terminals. Each subscriber terminal also includes a controller and an authorization memory which has a plurality of memory locations containing authorization data defining the levels of service for which the subscriber has paid. Unscrambling means in the individual subscriber terminal decoders are controlled by the authorization memory for selectively enabling unscrambling and viewing of scrambled television signals sent from the cable head-end. In some systems, television signals are transmitted from the head-end with a program tag, included in a data packet, that identifies a particular single-bit memory location in the subscriber terminal authorization memory. The corresponding memory location stores either a logic "1" or "0" bit establishing whether the subscriber is authorized or not authorized, respectively, for receiving the accompanying program. In the IPPV system of the invention, the data packet also includes an IPPV program tag which identifies a memory location in the subscriber terminal authorization memory that may be the same or different from the memory location identified by the program tag. A received non-zero IPPV tag results in a suitable display on the subscriber terminal decoder for indicating that the program associated with the IPPV tag may be bought in response to the subscriber taking appropriate action. In the preferred embodiment, the appropriate action consists of the subscriber using a personal password to access the authorization memory and set the memory location defined by the IPPV tag to "1" thereby self-authorizing the terminal for receiving the program. On a periodic basis, the head-end "polls" each subscriber terminal in the system for reading the contents of their respective authorization memories. The subscriber terminals individually respond by transmitting authorization memory information to enable the head-end to determine the status of the memory location or locations defined by the IPPV tag or tags. Based upon the memory information, the head-end determines whether the subscriber "bought" one or more IPPV programs and thereby the amount that is to be billed for such special event programming.
As will be seen, the program tag controls unscrambling of the accompanying signal by reading the authorization memory, whereas the IPPV tag controls self-authorization and the display by permitting writing to the authorization memory. The tags are independent of each other and give the head-end a great deal of flexibility in modes of operation.
With the system, subscriber terminal authorization memories of very limited size may be utilized to support an IPPV system. It will be appreciated that more than one IPPV tag may be used in the system by appropriate selection of different memory locations for different special programs.